Resonator structure



Feb. 3, 1953 A. M. GUREWITSCH 2,627,552

RESONATOR STRUCTURE Filed March so, 1950 Inventor: Anatole M.Gur-ewitsch,

by )gl/ 4% His Attorney.

Patented Feb. 3, 1953 RESONATOR STRUCTURE Anatole M. Gurewitsch, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 30, 1950, Serial No. 152,832

Claims.

The present invention relates to high frequency resonators, particularly to resonators finding useful application in apparatus for imparting high energy to charged particles.

The invention is applicable in connection with apparatus of the type disclosed in United States Patent No. 2,485,409, granted October 18, 1949 to Herbert C. Pollock and Willem F. Westendorp and assigned to the assignee of this present invention. Such apparatus comprises means for initially accelerating charged particles by the action of a field produced by a time-varying magnetic flux and for thereafter producing continued acceleration by a localized electric field of cyclically varying character.

In one form of this apparatus, the means employed for producing the localized electric fields comprises a space resonant structure suitably located along the path of the charged particles within the region of the time-varying flux. This disposition of the resonant structure requires particular consideration in view of the space limitations involved and also necessitates the provision of an arrangement for preventing excessive eddy currents from flowing in such structure, Furthermore, the generally circular path followed by the charged particles during acceleration is usually enclosed by a toroidally-shaped vacuum vessel which, in certain application, is preferably evacuated and permanently sealed off from the atmosphere. In such event it is desirable to make provision for the external application of the localized electric fields in order to facilitate permanent sealing of the vacuum vessel.

Accordingly, one object of the present invention comprises the provision of a space resonant structure adapted to serve as an accelerating de vice in charged particle accelerators. A further object of the invention is to provide a space resonant structure capable of operating efficiently within a strong time-varying magnetic field. A further and more particular object of the invention comprises the provision of a space resonant structure capable of supplying localized high frequency electric fields for accelerating charged particles in an orbital path.

One form of the invention exemplary of the principles thereof more fully described and defined hereinafter includes a resonator having a plurality of conductive strips supported upon the outer surface of a tubular section of dielectric material to form an inner conductor and a plurality of conductive strips spaced and supported from said tubular section of dielectric material to form an outer conductor. The first mentioned plurality of conductive strips is discontinuous near one end to rovide a gap across which strong electric fields may be developed when the resonator is excited. Both the first mentioned plurality of conductive strips and the second mentioned plurality of conductive strips may be short circuited at certain positions to facilitate the procurement of desired operational characteristics.

The features of the invention desired to be protected herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawing, in which Fig. 1 is a partially sectionalized elevation of resonator structure having one section of the outer conductor removed and suitably embodying the present invention, and Fig. 2 is a cross section taken along line 2-2 of Fig. 1 with both sections of the outer conductor in proper position.

Referring now to both figures of the drawing, there is shown resonator structure comprising a portion of a closed toroidal vessel I of dielectric material which defines within its interior an annular chamber. The envelope I provides, in connection with charged particle accelerating apparatus such as that disclosed in the above-mentioned Pollock and Westendorp Patent 2,485,409, a circular orbit in which charged particles, e. g., electrons derived from a suitably energized source, may be accelerated to a high energy level. Attached to the outer surface of vessel I is a plurality of longitudinally extending strips 2 which may consist of a suitably conductive material such as copper. Conductive strips 2 may be attached to vessel I with a desired adhesive material, for example, an alkyd resin prepared by reacting a polybasic acid and a polyhydric alcohol, such as a resin being prepared from glycerol and phthalic anhydride. Conductive strips 2 are discontinuous near the upper end of the resonator structure to provide a gap 3 across which strong electric fields may be developed as will be described hereinafter. Peripheral loops 4 and 5 consisting of conductive material, such as cooper, are positioned adjacent gap 3, as shown, for the purpose ,of short-circuiting conductive strips 2 on both sides of gap 3.

Supported by vessel I is a longitudinally sectionalized member 6 formed of insulating material and comprising matching sections which may be secured together by means of bolts I of 'Westendorp patent.

insulating material extending through holes '8 and having nuts 9 of insulating material screwed upon the ends thereof. Attached to the inner surface of member 6 is a plurality of longitudinally extending, peripherally spaced apart conductive strips it! which may be secured to member 6 in a manner similar to that described in connection with the attachment of strips 2 to vessel I. Member 6 is tapered inwardly at both end portions 6' in order to provide a means of support upon vessel l and also to provide a means of connecting the ends of strips [8 to corresponding ends of strips 2. Strips It! should be spaced around the inner surface of member 6 to correspond with the spacing of strips 2 about the periphery of vessel I so that, when both sections of member 6 are in position, the ends of strips Ill will be connected to corresponding strips 2.

With a given radial distance between strips Ill and strips 2 and with the proper selection of longitudinal dimensions, the structure shown in "the drawing operates as a quarter-wave,

'in the energy level of such electrons may be effected in accordance with the principles disclosed in the aforementioned Pollock and Tuning of the resonator structure may be conveniently accomplished by moving member 6 longitudinally with respect to cap For the purpose of exciting the resonator structure there is shown an input connector ll of the concentric'line type which provides direct coupling from a source of high frequency oscillations (not shown) to the resonator structure.

nient Hi around which conductive material l I extends to make contact with conductive strips 10. "Tubulajrmember I2 may be adjustably secured'within slot l3 by means of a nut it which engages threads IS on the outer periphery of tubular 'member l2. An inner conductor ll extends through the bore of member 12 and makes-contact with strips 2 through a disk [2.

Inner conductor H comprises an outer portion l 8-and an inner portion l9 which are interconnected by a spring 20 and a sleeve 2! surrounding spring 20. Outer portion 18 is sealed to a glass b'ead 22 having a press fit within the bore ofmember 12 while inner portion is is slidably inserted through a glass bead 23 having a press -fit within the bore of member 12. Spring 26 is attached between the adjacent ends of outer portion-i8 and inner portion i9. Sleeve 2! is rigidly secured to outer portion 18 of conductor it by any convenient means such as solder but is slidably positioned aroundinner portion Hi to per- 'mit relative linear movement between portions 18 and I9, thereby assuring good contact beage across gap 3, there is shown a high frequency probe 25 which comprises an inner conductor 25 extending through a hole 27 in member 6 andbeing terminated by a disk 28 which capacitively couples with the high frequency fields existing within the resonator structure when it :is excited. An outer conductor is provided by conductive material 29, such as copper or silver, attached to the bore of a tubular member 39 of insulating material threadably engaged within a recess 3| in member 6. Conductive material 29 extends around the inner end of tubular member 3% and makes contact with strips Iii as shown. Inner conductor 26 is slidably positioned within the bore of tubular member 33 and hole 21 by means of a glass bead 32. Any suitable type of highfrequency voltage detector may be connected to probe 25 in order to indicate the magnitude of the fields existing within the resonator structure.

As has been mentioned heretofore, the resonator structure of the invention in its preferred application in connection with apparatus for the acceleration of charged particles is traversed by a time-varying magnetic field of high intensity, which, in the view shown in Fig. l, is essentially perpendicular to the plane of the paper. This means, of course, that eddy currents will be induced in conductive ,material "which is traversed by the time-varying magnetic field. If special provision is not made to minimize these eddy currents, they will have a deleteri u efiec'b upon the'ope'ration of theresonator as well as upon the :operation of the remainder of the accelerator apparatus. Consequently, any conductive material traversed by the time-varying magnetic field should be of sufficiently small width and thickness to prevent the generation of'excessive eddy currents therewithin. As will be observed from the foregoing description, the resonator structure of the invention employs thin conductive material throughout as a'means of conducting the high frequency currents.

These conductor need only have a thicknessof the order of the depth of penetration of the high frequency current which flows therein When the resonator structure is excited. As an order of magnitude the material may have a final thickness of about 1 to 1 /2 mils when the resonator is to be excited at 160 me.

ihe provision of longitudinally subdivided strips 2 and It! to form the inner and outer conductors respectively of the resonator structure of the invention comprises convenient and direct means of reducing eddy currents'induced therein by the time-varying magnetic field. While the structure as above-described operates with good efficiency in connection with apparatus for accelerating charged particles, some eddy currents 'still flow in strips 2 and ii) with the undesirable consequences of heating the strips and interfering with the distribution of the time-varying field. In addition, the operation of the resonator structure with subdivided inner and outer conductors is somewhat impaired in that the high ple these strips closely.

frequency excitation is rendered more diflicult.

If strips 2 are not connected to each other, and similarly if strips ID are not connected to each other, the structure presents electrically a number of coupled conductive members which are sufficiently loosely coupled to have a great number of undesirable modes. Peripheral conductive loops 4 and 5 adjacent gap 3 serve to interconnect or short-circuit strips 2 and thereby to cou- Similar close coupling of strips l may be secured by providing a peripheral conductive loop 33 around the inner surface of each section of member 6 opposite gap 3. Such a conductive loop in connection with conductive loops 4 and 5 not only serves to improve the high frequency characteristics of the resonator structure but also serves to compensate for eddy currents in accordance with the principles disclosed in my copending application Serial No. 130,054, filed November 29, 1949, which issued as United States Patent No. 2,579,315 on December 18, 1951, and assigned to the assignee of the present invention.

Structure 5 may be constructed in any manner well-known to those skilled in the art such as by molding plastic material having suitable insulating properties. It may also be formed by impregnating strips of glass cloth with a solventless varnish such as a resin formed for example from diethylene glycol maleate and diallyl phthalate, wrapping the impregnated glass cloth around suitable forms, and curing in accordance with principles well-known to those skilled in the art. Vessel should be formed from dielectric material having a low-high frequency loss coefficient since the high frequency ield which appears across gap 3 should couple efliciently through the wall of vessel I to an electron beam moving therewithin.

While the above description of the invention has referred to the construction of the inner and outer conductors of the resonator structure by securing longitudinally extending, peripherally spaced apart conductive strips to ve sel 1 and member 6 with adhesive material, it will be readily appreciated that alternative constructions may be employed. One such alternative comprises placing a layer of silver paint on vessel l and member 6 and thereafter baking to secure adherence of the paint to the respective surfaces. The thickness of such layers may be increased by repeated painting and baking, for the purpose of obtaining a layer of proper thickness. Thereafter the strips and gap may be formed by burning in grooves with a tungsten disk which is rolled along the conductive surface while carrying a heavy current through the contact area. It is also possible to form the strips and gap by masking during the painting operation.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In apparatus for the acceleration of charged particles the combination which comprises a toroidal vessel of dielectric material disposed within a time-varying magnetic field and adapted to enclose an orbital path along which charged particles may be accelerated, and a resonator structure for supplying a high frequency electric field to accelerate the charged particles including an inner conductor formed of conductive strips attached to the outer periphery of said toroidal vessel and a longitudinally sectionalized outer conductor supported by and enclosing a portion of said toroidal vessel, said outer conductor comprising sections of insulating material having conductive stripsattached along the inner surfaces thereof whereby the generation of eddy currents within said resonator by said time-varying magnetic field may be minimized.

2. In apparatus for the acceleration of charged particles the combination which comprises a sealed and evacuated toroidal vessel of dielectric material disposed within a time-varying magnetic field and adapted to enclose an orbital path along which charged particles may be accelerated, and an external resonator structure for supplying a high frequency electric field to accelerate the charged particles including an inner conductor formed of conductive strips attached to the outer periphery of said toroidal vessel and a demountable sectionalized outer conductor supported by and enclosing a portion of said toroidal vessel, said sectionalized outer conductor comprising insulating material having thin conductive strips attached along the inner surface thereof whereby the generation of eddy currents Within said resonator by said time-varying magnetic field may be minimized.

3. A resonator structure comprising an inner conductor which includes a plurality of conductive strips disposed in longitudinally extending peripherally spaced apart relationship upon the outer surface of a portion of a toroidal vessel of dielectric material adapted to enclose, an orbital path along which charged particles may be accelerated, said strips being discontinuous near one end to form a peripheral gap and being joined together adjacent said gap to form peripheral conductive loops on both sides of said gap, a longitudinally sectionalized outer conductor which includes matching sections of insulating material having a plurality of longitudinally extending peripherally spaced apart conductive strips disposed along the inner surfaces thereof, said outer conductor being tapered inwardly at both ends to contact said inner conductor whereby said outer conductor is sup.- ported by said toroidal vessel, and means for exciting said resonator.

4. A resonator structure comprising an inner conductor which includes a plurality of conductive strips disposed in longitudinally extending peripherally spaced apart relationship upon the outer surface of a portion of a toroidal vessel of dielectric material adapted to enclose an orbital path along which charged particles may be accelerated, said strips being discontinuous near one end to form a peripheral gap and being joined together adjacent said gap to form peripheral conductive loops on both sides of said gap, a longitudinally sectionalized outer conductor which includes matching sections of insulating material having a plurality of longitudinally extending peripherally spaced apart conductive strips disposed along the inner surfaces thereof, said last-mentioned strips being joined together opposite said gap to form a peripheral conductive loop and said outer conductor being tapered inwardly at both ends to contact said inner conductor whereby said outer conductor is supported by said toroidal vessel, and means for exciting said resonator.

5. A resonator structure comprising an inner conductor which includes a plurality of conductive strips disposed in longitudinally extending peripherally spaced apart relationship upon the outer surface of a portion of a toroidal vessel of dielectric material adapted to enclose an orbital path along which charged particles may be accelerated, said strips being discontinuous near :.one end to Lform :a peripheral gap and being ,joined together adjacent said gap to iorm peripheral conductive loops on both sides of said gap, a longitudinally sectionalized outer conductor whichincludes matching sections of insulatingmaterial havinga plurality of longitudinally extending peripherally spaced apart conductive strips disposed along the inner surfaces thereof, said outer conductor being tapered inwardly at both ends to contact saidinner conductor whereby said outer conductorris sup- ,ported .by'said toroidal vessel, means for exciting said resonator; and a probe for measuring the voltage which appears across said gap when said resonator is-excited including a concentric transv1.5

.mission '.1ine capacitiyely coupled .to said .res-

qonator.

ANATOLE .M. GUREWITSCH.

wREFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 1 Number Name Date 2,233,748 Bust Mar. 4, 1941 2,416,315 Hartman Feb.. 25, 1947 2,459,332 McCown Jan. 18, 1949 12,485,400 McArthur Oct. 18, 1949 2,513,921 .Di Toro July 4, 1950 

